Abstract: An apparatus for controlling the starting of a three phase load in its normal phase sequence. The apparatus is connected to the load in a predefined manner and has input terminals for receiving three phase electric energy through external supply lines. There is provided a device within the apparatus which automatically corrects the phase sequence of the electric energy supplied to the load. An open phase protection device is provided which allows the starting of the load in response to the absence of open phase in the received electric energy, and inhibits the starting of the load in response to the presence of open phase in the received electric energy due to, for example, breaking of an external supply line. In one embodiment, the apparatus is built into a submersible motor-pump assembly. The pump is always initiated to rotate its impeller in a proper direction for pumping, regardless of correct or incorrect phase connections between the external supply lines and the input terminals of the apparatus.

Abstract: A submersible pump especially usable for civil engineering works is provided in which a wear resistant protecting member is disposed at the portion opposing the backside of an impeller shroud to protect that portion from wear due to abrasion by earth and sand contained in the liquid handled by the pump. The protecting member is provided with holes or portions similar to holes which are adapted to surround the exposed portions of the bolts so as to prohibit the liquid flow from directly contacting the bolt portions with flowing speed or kinetic energy so that wear of the bolts is prevented.